Downstream output level and/or output level tilt compensation device between CATV distribution system and CATV user

ABSTRACT

A downstream bandwidth output level and/or output level tilt compensation device that can be inserted into a signal transmission line of a CATV system on a premise of a user. The device includes a tuner that identifies low and high band signal channels, and a channel analyzer that determines a format of each of those channels. A signal measurement measures low and high band signal strengths. An offset circuit adds or subtracts an offset value to the low and/or high band channel signal strengths depending on whether the respective channel is analog or digital. A microprocessor compares the low and high band signal strengths, including any offset values, to a predetermined signal strength loss curve. A variable output level compensation device and a variable slope adjusting circuit are provided to amplify and adjust the gain slope of the downstream bandwidth.

BACKGROUND OF THE INVENTION

The use of a cable television (“CATV”) system to provide internet, voiceover internet protocol (“VOIP”) telephone, television, and radioservices is well known in the art. In providing these services, adownstream bandwidth (i.e., radio frequency (“RF”) signals, digitalsignals, optical signals, etc.) is passed from a supplier of theservices to a user and an upstream bandwidth is passed from the user tothe supplier. The downstream bandwidth is passed, for example, withinrelatively higher frequencies from within a total bandwidth of the CATVsystem while the upstream bandwidth is passed within relatively lowerfrequencies.

Traditionally, the size of the downstream bandwidth far exceeds the sizeof the upstream bandwidth due to nature of the services provided. Forexample, while the downstream bandwidth must accommodate all of thetelevision and radio programming along with internet and VOIPdownloading, the upstream bandwidth is only required to accommodateinternet, system control signals, and VOIP uploading. Problems arearising, however, due to an increase in upstream bandwidth usage causedby an increasing demand for higher speed internet uploads and theincreasing demand for the VOIP telephone services.

VOIP telephone services places significant demands on the upstreambandwidth. When a user uploads a large image file to a photo sharingwebsite, the image file will be parsed into a number of data packetsthat can be intermixed with other data packets being passed through aparticular portion of the upstream bandwidth by other users located on aparticular signal transmission line within the CATV system. To optimizea total data throughput on the particular signal transmission line, thedata packets may be significantly delayed and/or reorganized without anyknowledge of or inconvenience to the user. When a user uses VOIPtelephone services, their voice is converted into data packets that aresimilar in form to the data packets used to upload the image file.Because a typical conversation is carried out in real time, meaning thata contiguous and unbroken flow of data packets is required, any personwith whom the user is talking will quickly notice significant delays inthe delivery of the data packets and/or reorganization of the datapackets that results in audio distortion of the user's voice. Any suchreorganization and/or delay in the uploading of data packets carryingVOIP telephone services are measured in terms of jitter, and are closelymonitored because of the significant service quality characteristics itrepresents.

Jitter experienced between the user and their caller is a direct resultof network congestion within the upstream bandwidth. Because theupstream bandwidth is shared by all users on the particular signaltransmission line, each user is competing with the other users forpacket data space within the upstream bandwidth. Even further, each ofthe users can unknowingly inject interference signals, such as noise,spurious signals, and other undesirable signals, into the upstreambandwidth through the use of common household items and poor qualitywiring in the user's premise, the interference signals causing errorsthat force a slow down and an additional amount of jitter in theupstream flow of packets.

In an effort to increase the upstream flow of packets, several suppliershave a plan to increase the size of the upstream bandwidth from 5-42 Mhzto 5-85 Mhz to allow a greater flow of the upstream content. Along withsuch an increase, the downstream bandwidth must be correspondinglydecreased in size because the total bandwidth is relatively fixed. Sucha change is, however, very difficult to implement.

Traditional practices would require that every drop amplifier and twoway (diplex) filter in network amplifiers and nodes of the CATV systemto be changed as part of the increasing the size of the upstreambandwidth. Compounding the difficulty of implementing such a change, allof the changes must be implemented at various locations throughout theCATV system at a single, particular time. Accordingly, such animplementation is time consuming, costly, and difficult to coordinate.

Further, while increasing the size of the upstream bandwidth mayincrementally increase the flow of upstream data packets, the upstreambandwidth remains susceptible to reliability/congestion issues since itis based on an inherent, system wide flaw that leaves the upstreambandwidth open and easily impacted by any single user. For example,while the downstream bandwidth is constantly monitored and serviced byskilled network engineers, the upstream bandwidth is created and passedusing an infrastructure within a user's premise that is maintained bythe user without the skill or knowledge required to reduce the creationand passage of interference signals into the upstream bandwidth. Thisissue is further compounded by the fact that over 500 premises can beconnected together such that interference signals generated by one ofthe 500 premises can easily impact all of the remaining premises. It iscommon in the art for the supplier to add physical filters between theuser's premise and a tap from of the main signal distribution systemnear the users premise to reduce the impact of the interference signalsgenerated on the user's premise, but such a physical filter must beinstalled manually and does not account for significant, transientinterference sources such as garbage disposals, vacuum cleaners,welders, powered hand tools, etc.

Even further, increasing the size of the upstream bandwidth forcessuppliers to push their downstream content into increasingly higherfrequency portions of the downstream bandwidth. Unfortunately, thesehigher frequencies are much more susceptible to parasitic losses insignal strength caused by the signal transmission lines, connectors onthe user's premise, devices connected to the signal transmission lineson the user's premise, etc. In the past many users have added relativelylow-tech drop amplifiers on their premise to account for such losses.Because of the changes to increase the size of the upstream bandwidth,all of these drop amplifiers must be removed and or replaced.Additionally, because of the increased demands placed on the downstreamcontent (e.g., high definition television, increased compression, etc.)the signal strength (i.e., level) of the downstream bandwidth must bemaintained to closer tolerances than can typically be provided by thetypical low-tech drop amplifier. Accordingly, as a result of increasingthe size of the upstream bandwidth, the quality of the content moved tothe higher frequencies within the downstream bandwidth may besignificantly lessened causing a decrease in customer satisfaction andan increase in costly service calls.

In light of the forgoing, increasing the size of the upstream bandwidth:(i) may require a significant amount of capital expenditure in terms newfilter devices and the manpower to install the devices; (ii) may notresult in the expected large increases in upstream data throughputbecause of the interference signals injected from within each user'spremise; (iii) may result in lower quality downstream content, and (iv)may inject additional interference signals that now fall within theadditional upstream bandwidth, which would have otherwise been filteredout.

SUMMARY OF THE INVENTION

The present invention helps to increase the signal quality of thedownstream bandwidth by reducing the effect of parasitic lossesoccurring within the CATV distribution system. The present invention isspecifically adapted to be placed on a user's premise so that it canmeasure the downstream bandwidth an provide an appropriate amount ofoutput level compensation and an appropriate amount of slope adjustment.These amounts of output level compensation and slope adjustment ensuresthat the user has receives a high quality downstream bandwidth andensures that the CATV supplier will not be required to perform costlyservice calls relating to a poor quality downstream bandwidth.

In accordance with one embodiment of the present invention, a downstreambandwidth output level and/or output level tilt compensation device isprovided that can be inserted into a signal transmission line of a CATVsystem on a premise of a user. The device includes a tuner configured toscan a downstream bandwidth to identify a low band signal channel and ahigh band signal channel and a channel analyzer configured to determinea format of each of the low band channel and the high band channel. Thedevice further includes a signal measurement device configured tomeasure a low band signal strength of the low band channel and a highband signal strength of the high band channel, and an offset circuit.The offset circuit is configured to perform at least two of: (i) add anoffset value to the low band signal strength when the low band channelis a digital format; (ii) subtract an offset value from the low bandsignal strength when the low band channel is an analog format; (iii) addan offset value to the high band signal strength when the high bandchannel is the digital format; and (iv) subtract a gain offset valuefrom the high band signal strength when the high band channel is theanalog format. The device further includes a microprocessor configuredto compare the low band signal strength and the high band signalstrength, including any offset values, to a predetermined signalstrength loss curve. The device further includes a variable output levelcompensation device, and a variable slope adjusting circuit.

In accordance with one embodiment of the present invention, a CATVsystem is provided for supplying CATV services from a supplier to aplurality of users. The system includes at least one discrete downstreambandwidth output level and/or output level tilt compensation device thatcan be inserted into a signal transmission line of the CATV system on apremise of each user. Each device is inserted into the signaltransmission line and each device includes a tuner configured to scan adownstream bandwidth to identify a low band signal channel and a highband signal channel and a channel analyzer configured to determine aformat of each of the low band channel and the high band channel. Thedevice further includes a signal measurement device configured tomeasure a low band signal strength of the low band channel and a highband signal strength of the high band channel, and an offset circuit.The offset circuit is configured to perform at least two of: (i) add anoffset value to the low band signal strength when the low band channelis a digital format; (ii) subtract an offset value from the low bandsignal strength when the low band channel is an analog format; (iii) addan offset value to the high band signal strength when the high bandchannel is the digital format; and (iv) subtract a gain offset valuefrom the high band signal strength when the high band channel is theanalog format. The device further includes a microprocessor configuredto compare the low band signal strength and the high band signalstrength, including any offset values, to a predetermined signalstrength loss curve. The device further includes a variable output levelcompensation device, and a variable slope adjusting circuit.

In accordance with one embodiment of the present invention, the variableoutput level compensation device and the variable slope adjustingcircuit are configured such that a gain associated with the high bandchannel is greater than a gain associated with the low band channel.

In accordance with one embodiment of the present invention, thepredetermined signal strength loss curve is a standard loss curverepresentative of the transmission line used on or near the premise ofthe CATV subscriber.

In accordance with one embodiment of the present invention, the tuner isconfigured to scan from a maximum frequency toward lower frequencies tofind the high band channel, and is configured to scan from a minimumfrequency toward higher frequencies to find the low band channel.

In accordance with one embodiment of the present invention, an amount ofsignal level adjustment provided by the variable output levelcompensation device is determined based on the high band signalstrength.

In accordance with one embodiment of the present invention, an amount ofslope adjustment provided by the variable slope adjusting circuit isdetermined based on the low band signal strength.

In accordance with one embodiment of the present invention, the signalmeasurement circuit is arranged to measure the high band signal strengthand the low band signal strength downstream from the variable outputlevel compensation device.

In accordance with one embodiment of the present invention, a method isprovided for conditioning a downstream bandwidth on a premise of a userof CATV services. The method includes receiving a downstream bandwidthfrom a CATV supplier, scanning the downstream bandwidth to obtain a lowband channel and a high band channel, and measuring a low band signalstrength of the low band channel and a high band signal strength of thehigh band channel. The method further includes determining a format ofthe low band channel, determining a format of the high band channel, andoffsetting one of the low band signal strength and the high band signalstrength by a predetermined offset value when one of the low bandchannel and the high band channel is an analog format and one of the lowband channel and the high band channel is a digital format. The methodfurther includes comparing the low band signal strength, and the highband signal strength, including any offset values, to a predeterminedsignal strength loss curve. The method further includes providing anamount of output level compensation, and providing an amount of slopeadjustment.

In accordance with one embodiment of the present invention, the amountof slope adjustment is such that a gain associated with the high bandchannel is greater than a gain associated with the low band channel.

In accordance with one embodiment of the present invention, thepredetermined signal strength loss curve is a standard loss curverepresentative of a signal transmission line used on or near a premiseof a subscriber.

In accordance with one embodiment of the present invention, the scanningis performed such that a scan begins from a maximum frequency andextends toward lower frequencies to find the high band channel, and suchthat a scan begins from a minimum frequency and extends toward higherfrequencies to find the low band channel.

In accordance with one embodiment of the present invention, the amountof output level compensation is determined based on the high band signalstrength.

In accordance with one embodiment of the present invention, the amountof slope adjustment is determined based on the low band signal strength.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the invention,references should be made to the following detailed description of apreferred mode of practicing the invention, read in connection with theaccompanying drawings in which:

FIG. 1 is a graphical representation of a CATV system arranged inaccordance with an embodiment of the present invention;

FIG. 2 is a graphical representation of a user's premise arranged inaccordance with an embodiment of the present invention;

FIG. 3 is a partial circuit diagram of a premise device made inaccordance with an embodiment of the present invention;

FIG. 4 is a partial circuit diagram of the premise device represented inFIG. 3;

FIG. 5 is a circuit diagram representing a premise device including aconfigurable frequency band selection device made in accordance withanother embodiment of the present invention;

FIG. 6 a is a circuit diagram representing a premise device including anupstream bandwidth conditioning device made in accordance with anotherembodiment of the present invention;

FIG. 6 b is a circuit diagram representing a premise device including anupstream bandwidth conditioning device made in accordance with anotherembodiment of the present invention;

FIG. 7 is a flow chart representing an signal level adjustment settingroutine performed by the circuit of FIGS. 6 a and 6 b;

FIG. 8 is a circuit diagram representing a premise device including anautomatic downstream bandwidth output level and/or output level tiltcompensation device made in accordance with another embodiment of thepresent invention; (NOTE: manually inserted compensation devices havebeen common for years)

FIG. 9 is a graphical representation of an interpolated gain curvedetermined in accordance with the device represented in FIG. 8.

FIG. 10 is a graphical representation of a gain curve determined inaccordance with the device represented in FIG. 8;

FIG. 11 is a graphical representation of a gain curve determined inaccordance with the device represented in FIG. 8;

FIG. 12 is a graphical representation of a gain curve determined inaccordance with the device represented in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a cable television (“CATV”) system typicallyincludes a supplier 20 that transmits downstream signals, such as radiofrequency (“RF”) signals, digital signals, optical signals, etc., to auser through a main signal distribution system 30 and receives upstreamsignals from a user through the same main signal distribution system 30.A tap 90 is located at the main signal distribution system 30 to allowfor the passage of the downstream\upstream signals from\to the mainsignal distribution system 30. A drop transmission line 120 is then usedto connect the tap 90 to a house 10, 60, an apartment building 50, 70, acoffee shop 80, and so on. A premise device 100 of the present inventionis connected in series or in parallel between the drop transmission line120 and a user's premise distribution system 130.

Referring still to FIG. 1, is should be understood that the premisedevice 100 can be placed at any location between the tap 90 and theuser's premise distribution system 130. This location can beconveniently located within the building 10, or exterior to the building60. Similarly, the premise device 100 can be located within individualapartments of the apartment building 70 or exterior to the apartmentbuilding 50. It should be understood that the premise device 100 can beplaced at any location, such as the coffee shop 80 or other business,where CATV services, including internet, VOIP, or otherunidirectional\bidirectional services are being used.

As shown in FIG. 2, the user's premise distribution system 130 can thenbe split using a splitter 190 so that upstream/downstream signals canpass to a television 150 and a modem 140 in accordance with practiceswell known in the art. The modem 140 can include voice over internetprotocol (“VOIP”) capabilities affording telephone 170 services and caninclude a router affording internet services to a desktop computer 160and a laptop computer 180, for example.

Additionally, it is common practice to provide a “set-top box” (“STB”)or “set-top unit” (“STU”) for use directly with the television 150. Forthe sake of clarity, however, there is no representation of an STB orSTU included in FIG. 2. The STB and STU are mentioned here in light ofthe fact that many models utilize the upstream bandwidth to transmitinformation relating to “pay-per-view” purchases, billing, etc.Accordingly, it should be understood that even though FIG. 2 explicitlyshows that there is only one premise device 100 used for each devicegenerating upstream data packets, each premises device 100 can be usedwith two or more devices (e.g. a modem, a STB, a STU, a dedicated VOIPserver, etc.) that transmit upstream data packets via the upstreambandwidth.

Referring to FIG. 3, the premise device 100 includes a main circuit 200that is positioned along with a tuner circuit 600 and a microprocessorcircuit 800. Preferably, the combination of circuits 200, 600, 800 formsa configurable frequency band selection device 1 (represented separatelyin FIG. 5), an upstream bandwidth conditioning device 2 (representedseparately in FIGS. 6 a and 6 b) and a downstream output level and/oroutput level tilt compensation device 3 (represented separately in FIG.8), each of which will be discussed separately in greater detail below.It should be understood, however, that circuits 200, 600, 800 of thepremise device 100 can be configured to form any combination of thedevices such that the premise device 100 may include any one of thedevices, any two the devices, or all three of the devices. Preferably,each of the circuits are positioned within a single enclosure, but itshould be understood that circuits 200, 600, 800 could be arrangedwithin multiple enclosures to account for space, cost, better resultantperformance, or other environmental considerations.

Because a diagram of a premise device 100 including all three devices istoo complex to be clearly represented in one figure, a circuit 205 ofthe main circuit 200, as it is represented in FIG. 3, is represented inFIG. 4 with inputs and outputs between itself and the remainingpositions of the circuit 200 in FIG. 3 labeled similarly.

Along these lines, alternate embodiments of the premise device 100 arerepresented in FIGS. 5, 6 a, 6 b and 8. FIG. 5 represents an embodimentof the premise device 100 including only the configurable frequency bandselection device 1. FIGS. 6 a and 6 b represent an embodiment of thepremise device 100 including only the upstream bandwidth conditioningdevice 2. FIG. 8 represents an embodiment of the premise device 100including only the downstream output level and/or output level tiltcompensation device 3. It should be understood that the embodimentsshown in FIGS. 5, 6 a, 6 b and 8 are presented to help clarify thecomponents specific to the particular device, and that other embodimentsincluding combinations of these are envisioned.

Individual components that are similar between the embodimentsrepresented in FIGS. 3, 4, 5, 6 a, 6 b, and 8 are identified using thesimilar reference numbers. For example, the microprocessor representedin each of the embodiments is referenced using the number 810. Oneskilled in the art should know that the microprocessor could be the sameor different across the embodiments depending on the requirements placedthereon.

As shown in FIG. 3, the main circuit 200 of the premise device 100includes a supplier side 210 and a premise side 220. The supplier side210 is positioned to receive the downstream bandwidth from the supplier20 (FIG. 1) and to send the upstream bandwidth to the supplier 20. Thepremise side 220 is positioned to send the downstream bandwidth to theuser and to receive the upstream bandwidth from the user. Each of thesupplier side 210 and the premise side 220 can include a traditionalthreaded 75 ohm connector so that the premise device 100 can be easilyplaced in series with the drop transmission line 120 and the premisedistribution system 130. Alternatively, each of the supplier side 210and the premise side 220 may include a proprietary connecter to hinderattempts at tampering with or theft of the premise device 100. Otherconnectors may also be used depending on the type and/or size of thedrop transmission line 120, the premise distribution system 130, or asystem impedance other than 75 ohms.

The premise device 100 preferably includes a lightening protectiondevice 230 positioned near the supplier side 210 and a lighteningprotection device 240 positioned near the premise side 220. Having twolightening protection devices 230, 240 attempts to protect the premisedevice 100 from energy passing from the drop transmission line 120 froma lighting strike and from energy passing from the premise distributionsystem 130 from a lighting strike. It should be understood that thelightening protection devices may not be necessary if/when the premisedevice 100 is configured to be placed in a CATV system that utilizesnon-conductive signal transmission lines. Any of the high quality,commercially available lightning protection devices will function wellwithin the specified locations within the premise device 100.

The premise device 100 preferably includes two power bypass failureswitches 250, 260 that route all of the upstream\downstream signalsthrough a bypass signal path 270 (e.g. a coaxial cable, an opticalcable, a microstrip, a stripline, etc.) in the event of a power outage.The bypass failure switches 250, 260 are preferably located near thesupplier end 210 and premise end 220, respectively. In an effort toprotect the bypass failure switches 250, 260 from damage due tolightening energy, they are preferably placed between the lighteningprotection devices 230, 240 and the supplier end 210 and premise end220.

Each of the bypass failure switches 250, 260 includes a default positionbypassing the upstream/downstream signals through the bypass signal path270 at any time power is removed from the premise device 100. When poweris applied, each of the bypass failure switches 250, 260 actuate to asecond position that disconnects the bypass signal path 270 and passesall of the upstream\downstream signal transmissions along another paththrough the circuit 205 (FIG. 4) within the main circuit 200. Theswitches may also be controlled such that when there is a fault detectedin the premise device 100 that could abnormally hinder the flow of theupstream\downstream bandwidths through the circuit 205 (FIG. 4), theswitches 250, 260 are moved to their default position sending theupstream/downstream signal transmissions through the bypass signal path270. Any of the high quality, commercially available signal transmissionswitches will function well within the specified locations within thepremise device 100. The bypass signal path 270 can be any suitablecoaxial cable or optical cable depending on the CATV systemconfiguration.

The premise device 100 preferably includes circuit components creatingthe frequency band selection device 1 (FIG. 5 and represented but notreferenced in FIGS. 3 and 4). The frequency band selection device 1 isconfigured to automatically switch between a configuration correspondingto earlier Data Over Cable Service Interface Specification (“DOCSIS”)specifications and a configuration corresponding to a later generationspecification, such as DOCSIS 3.0. While this feature may beadvantageous by itself in the premise device 100, this feature allowsfor other devices, such as the upstream bandwidth conditioning device 2and the downstream bandwidth output level and/or output level tiltcompensation device 3, to remain relevant after a change betweenspecifications. In particular, because each of these devices requires anaccurate separation of signals between the upstream bandwidth and thedownstream bandwidth, any necessary change in the upstream/downstreambandwidths would render these specific devices inoperable. It should beunderstood that even though the DOCSIS specifications are referencedabove and below, the upstream/downstream bandwidth configurations may bemaintained and changed according to any specifications.

A simplified version of the of the frequency band selection device 1 isshown in FIG. 5 while all of the components are also present in theembodiment of FIGS. 3 and 4. The selection device 1 includes a pluralityof switches 280, 290, 300, 310, 320, 330 that define a first signal pathset 910 and second signal path set 920. Each signal path set includestwo discrete signal paths, a high frequency signal path 930 and a lowfrequency signal path 940. The first signal path set 910 is formed usinga pair of first frequency band splitting devices 340, 345, and thesecond signal path set 920 is formed using a pair of second frequencyband splitting device 350, 355. A cutoff frequency set by the first pairof frequency band splitting devices 340, 345 corresponds to DOCSISspecifications having a narrower upstream bandwidth, and a cutofffrequency set by the second set pair of frequency band splitting devices350, 355 corresponds to the later DOCSIS specifications, which include abroader upstream bandwidth than the earlier DOCSIS standards. It shouldbe understood that the cutoff frequencies can be changed to accommodateeven newer DOCSIS standards or other standards by the mere replacementof the first pair of frequency band splitting devices 340, 345 and/orthe second pair of frequency band splitting devices 350, 355. Any of thehigh quality, commercially available switches and frequency bandsplitting devices will function well within the specified locationswithin the premise device 100.

Each of the switches 280, 290, 300, 310, 320, 330 is controlled eitherdirectly or indirectly by a microprocessor 810 (FIG. 3). Themicroprocessor 810 determines whether to actuate the switches 280, 290,300, 310, 320, 330 to the first signal path set 910 or to the secondsignal path set 920 based on an information transmission signalpreferably sent by the supplier 20. A signal coupler 360 allows for areceiver to 820 to receive the information transmission signal, such asa tone, a coded operational signal, or other well known informationtransmission, that can be understood by the microprocessor 810 toindicate the switch position. For example, the presence of aninformation signal can be used to indicate that the microprocessor 810should select the second signal path set 920, whereas no informationsignal could indicate that microprocessor 810 should select the firstsignal path set 910. For example, the presence of a continuous tone at900 MHz can be identified by passing a signal carrying such a tonethrough a band pass filter 830 to eliminate unnecessary signals and acomparator 840, which only provides a tone to the microprocessor when/ifthe tone is stronger than a predetermined threshold determined by avoltage source 850 and a resistive voltage divider 860. The frequencycan be selected by the microprocessor 810 and can be tuned by aphase-locked loop control system 880 and an amplifier 870 in a mannerwell known in the art. Any of the high quality, commercially availablemicroprocessors, signal couplers and receivers will function well withinthe specified locations with the premise device 100.

The premise device 100 preferably further includes circuit componentscreating the upstream bandwidth conditioning device 2, whichautomatically increases the signal to noise ratio of the upstreambandwidth created on the user's premise and passed into the upstreambandwidths on the main signal distribution system 30. It should beunderstood that with VOIP telephone service, the consistent flow ofupstream data packets that lasts as long as the telephone call canappear to be noise (i.e., interference signals). Before VOIP, suchcontinuous upstream flow data of data packets was not likely.Accordingly, the present device purposefully includes logic andstructure that will halt the addition of attenuation once the maximumoutput of the cable modem is sensed even if the upstream data flow isconsistent enough to be interpreted as noise.

As shown in FIGS. 3, 4, and 6 a, the upstream bandwidth conditioningdevice 2 of one embodiment of the premise device 100 includes a variableattenuator 400 and an amplifier 410. The amount of signal leveladjustment used to condition the upstream bandwidth is determined by themicroprocessor 810 based on inputs from a signal level detector 390. Thesignal level detector 390 measures and maintains a contemporary peaksignal strength of the upstream bandwidth via a tap 370 and a filter380. The microprocessor 810 includes a counting circuit, a thresholdcomparison circuit and a level comparison circuit. It should beunderstood that even though a microprocessor 810 is used in the presentembodiment, it is envisioned to control the variable attenuator 400 inthe manner described using a traditional logic circuit.

As shown in FIG. 6 b, another embodiment of the upstream bandwidthconditioning device 2 includes a variable amplifier 415, which isconnected and controlled by the 810. According to this embodiment, anattenuator 405 is present and is not controlled by the microprocessor.Other embodiments are envisioned that include both a variable amplifier415 and a variable attenuator 405. Further, the variable signal leveladjustment device could also be an automatic gain control circuit(“AGC”) and function well in the current device. In other words, itshould also be understood that the amount of signal level adjustment andany incremental amount of additional signal level adjustment can beaccomplished through any of a wide variety of amplification and/orattenuation devices.

In light of the forgoing, the term “variable signal level adjustmentdevice” used herein should be understood to include not only a variableattenuation device, but also circuits containing a variable amplifier,AGC circuits, other variable amplifier/attenuation circuits, and relatedoptical circuits that can be used to reduce the signal strength on theupstream bandwidth.

It should be noted that the term contemporary signal strength isintended to describe a current or present signal strength as opposed toa signal strength measured at a time in the past (i.e., a previoussignal strength) such as prior to an application of signal leveladjustment or an application of an additional amount of signal leveladjustment. The reason for this point should be clear based on thefollowing.

In operation, the microprocessor 810 within the upstream bandwidthconditioning device 2 performs a signal level setting routine 1000 (FIG.7) to determine an appropriate amount of signal level adjustment toapply to the upstream bandwidth via the variable attenuator 400, thevariable amplifier 415 or other suitable variable signal leveladjustment device. The signal level setting routine can be runcontinuously, at predetermined intervals, and/or on command as a resultof an information signal transmitted by the supplier 20. Once initiated,the microprocessor 810 or logic circuit performs the signal levelsetting routine in accordance with the flow chart shown in FIG. 7.

Referring now to FIG. 7, upon initialization 1010 of the signal levelsetting routine 1000, the counting circuit in the microprocessor 810 isreset to zero (0), for example, in step 1020. Next, the microprocessor810 iteratively performs steps 1030, 1040, 1050, 1060, 1070, 1080 and1090 until the counter reaches a predetermined number (e.g. 25) or theanswer to step 1080 is negative.

Specifically, in step 1030 the microprocessor 810 reads a contemporarysignal strength from the signal level detector 390, and the counter isincremented by a predetermined increment, such as one (1) in step 1040.The microprocessor 810 then looks to see if the counter is greater thanthe predetermined number (i.e., 25). If so, the microprocessor 810 endsthe routine, but if not, the microprocessor 810 proceeds to step 1060.In step 1060, the microprocessor 810 compares the contemporary signalstrength to a predetermined threshold. If the contemporary signalstrength is greater than the predetermined threshold, the microprocessor810 instructs the variable attenuator 400 to add an amount of additionalsignal level adjustment (e.g. 1 dB), but if the contemporary signalstrength is lower than the predetermined threshold, the microprocessor810 returns to step 1030.

After adding the amount of additional signal level adjustment, themicroprocessor 810 reads a new contemporary signal strength in step 1080while saving the previously read contemporary signal strength (i.e.,from step 1030) as a previous signal strength in preparation for step1090. In step 1090, the microprocessor 810 compares the contemporarysignal strength measured in step 1080 and the previous signal strengthmeasured in step 1030 to one another. If the contemporary signalstrength is equal to the previous signal strength then themicroprocessor 810 returns to step 1030, but if the contemporary signalstrength is less than the previous signal strength the microprocessor810 proceeds to step 1100 where it instructs the variable attenuator 400to reduce the amount of signal level adjustment by a predeterminedamount (e.g. the amount of additional signal level adjustment added instep 1070 or an amount greater than the additional signal leveladjustment added in step 1070). After step 1100, the microprocessor 810saves the total amount of signal level adjustment in step 1110 and stopsthe routine at step 1120. Again, it should be understood that the amountof additional signal level adjustment may be added/removed by thevariable amplifier 415, or by the AGC discussed above.

As mentioned above, an important aspect of the present signal levelsetting routine is the comparison step conducted in step 1090. Atraditional cable modem 140 (FIG. 2) used in CATV systems can adjust itsoutput level based on information signals received from the suppler inthe downstream bandwidth. In particular, if the modem signal received bythe supplier 20 is weak, the supplier 20 instructs the modem 140 toincrease its transmission signal level. As this relates to the currentinvention, the modem 140 will continually increase signal level as aresult of increased amounts of upstream bandwidth signal leveladjustment until the modem 140 can no longer increase its transmissionsignal strength. Accordingly, the contemporary signal strength measuredin step 1080 after the addition of additional signal level adjustment instep 1070 should be equal to the previous signal strength if the modem140 is able to compensate for the additional signal level adjustment.However, if the modem 140 is already producing its maximum signalstrength, the contemporary signal strength will be less than theprevious signal strength when an additional amount of upstream bandwidthsignal level adjustment is applied.

Because problems could result in the modem 140 from operating it at itsmaximum output (i.e., signal distortion may be high when the modem 140is operating at or near a maximum level and/or the durability of themodem 140 may be sacrificed when the modem 140 is operating at or near amaximum level), the amount of signal level adjustment may be reduced bya sufficient amount in step 1100 to ensure quality of the output signalgenerated by the modem 140 and the durability of the modem 140 once themaximum output strength of the modem 140 is identified.

It is noted that in a system with more than one device passing datapackets into the upstream bandwidth, the premise device 100 may identifythe maximum output strength of one device and not the other. In otherwords, the premise device 100 may identify the first device achievingits maximum output strength without proceeding to identify the maximumoutput strength of any other devices. If the premise device 100 fails toidentify the first observed maximum output strength, that device maycontinue to operate at its maximum output strength until anotherdetermination cycle is initiated.

The predetermined number compared in 1050 can be related directly to theamount of signal level adjustment. For example, if the variable signallevel adjustment device is a step attenuator including 25 steps of 1 dBattenuation, as is the case in the embodiment represented in FIG. 6 a,the predetermined number can be set to 25 to allow for the finestresolution (i.e., 1 dB) and the broadest use of the particular stepattenuator's range (i.e., 25 dB). It should be understood that thenumber of steps could be reduced and the resolution could be decreased(i.e., 5 steps of 5 dB) if faster overall operation is desired. It isalso foreseeable that the predetermined number could be increased if avariable signal level adjustment device having a finer resolution (i.e.,less than 1 dB) or a broader range (i.e., greater than 25 dB) isutilized. The incremented amount discussed here relating the counter andthe predetermined number is one (1) such that there are 25 iterations(i.e., 25 steps) when the predetermined number is 25. The incrementcould easily be any number (i.e., 1, 5, 10, −1, −10, etc.) depending onthe predetermined number and the total number of steps desired, which,as discussed above, is based on the desired resolution and the desiredrange of signal level adjustment.

The amount of additional attenuation added in step 1070, and thepredetermined amount of attenuation reduced in step 1100 are allvariables that are currently based, at least partially, on hardwaredesign limitations and can, depending on the hardware, be adjusted byone skilled in the art based on the conditions experienced in aparticular CATV system and with particular CATV equipment. As discussedabove, the variable signal level adjustment device in one embodiment ofthe present invention is a step attenuator having a resolution of 1 dBand a range of 25 dB. Accordingly, the amount of additional attenuationadded in step 1070 using the present hardware could be 1 dB or multiplesof 1 dB. Similarly, the predetermined amount of attenuation reduced instep 1100 can be 1 dB or multiples of 1 dB. It should be understood thatif the amount of additional attenuation added in step 1070 is a multipleof 1 dB, such as 5 dB, the amount of attenuation reduced in step 1100can be a lesser amount, such as 2 dB or 4 dB. The amount of attenuationreduced in step 1100 can also be greater than the amount of additionalattenuation added in step 1070 for the reasons stated above relating tomaintaining the quality of the output from the modem 140 and the anddurability of the modem 140.

The predetermined threshold compared in step 1060 is a signal levelsufficient to distinguish the presence of upstream data packets in theupstream bandwidth from interference signals. This value will varydepending on the output power of any cable modem 140, STB, STU, etc. inthe system and the average observed level of interference signals. Agoal is, for example, to determine if a device is present that sendsupstream data packets via the upstream bandwidth. If the predeterminedthreshold is set too low, the interference signals may appear to beupstream data packets, but if the predetermined threshold is set toohigh, the upstream data packets may appear as interference signals.

Any of the high quality, commercially available signal couplers, signallevel detectors, variable attenuation devices, filters, amplifiers, andmicroprocessors will function well within the specified locations withinthe premise device 100.

Referring now to FIGS. 3, 4, and 8, the premise device 100 preferablyincludes circuit components creating the downstream bandwidth outputlevel and/or output level tilt compensation device 3, which helps tomaintain a desired signal quality in transmitted signals usingrelatively high frequencies within the downstream bandwidth, which aremuch more susceptible to traditional parasitic losses. At a simplisticlevel, the microprocessor 810 observes channel data obtained from thetuner circuit 600, compares the observed channel data to a knownparasitic loss curve, and then adjusts a pair of variable output levelcompensation devices 440, 450 and a variable slope adjusting circuit 460located in the circuit 200 to create an output having a desired gaincurve (i.e., a curve representative of transmitted signal strengths)across the downstream bandwidth. While each of the variable output levelcompensation devices 440, 450 are depicted in FIGS. 4 and 8 as avariable attenuator, it should be understood that the term “variableoutput level compensation device” used herein should be understood toinclude not only a variable attenuation device, but also circuitscontaining a variable amplifier, AGC circuits, other variableamplifier/attenuation circuits, and related optical circuits that can beused to alter the signal strength of signals in the downstreambandwidth. Each of these steps will be discussed in further detailbelow.

The tuner circuit 600 obtains the downstream bandwidth from a coupler420 drawing the downstream bandwidth off of the high frequency signalpath 930 (FIG. 5). Please note that these signals will be referred toherein as the coupled downstream bandwidth. The coupled downstreambandwidth is passed through a resistor 430 prior to being passed into atuner 610.

Through instructions provided by the microprocessor 810, the tuner 610scans the coupled downstream bandwidth in an effort to locate andidentify a channel having a low frequency, referred to herein as a lowband signal channel 1250 (FIG. 9), and a channel having a highfrequency, referred to herein as a high band signal channel 1260 (FIG.9). In the present instance, the microprocessor 810 instructs the tuner610 to begin at the lowest frequency in the downstream bandwidth andscan toward higher frequencies until the low band signal channel 1250 isfound. Similarly, the microprocessor 810 instructs the tuner 610 tobegin at the highest frequency in the coupled downstream bandwidth andscan toward lower frequencies until the high band signal channel 1260 isfound. Accordingly, the low band signal channel 1250 is a channellocated near the lowest frequency within the coupled downstreambandwidth while the high band channel 1260 is a channel located near thehighest frequency within the coupled downstream bandwidth. Even thoughthe low band signal channel 1250 and the high band signal channel 1260are depicted in FIG. 9 as a single frequency for clarity, it should beunderstood that a channel is typically a range of frequencies. It shouldalso be understood that the low band signal channel 1250 and the highband signal channel 1260 do not need to be the lowest or highestfrequency channels, respectively. It is beneficial, however that the twochannels be spaced as far apart from one another as practical to betterestimate the amount of parasitic loss experiences across the entiredownstream bandwidth.

During the scanning process to locate and identify the low and high bandsignal channels 1250, 1260, the tuner circuit 600 provides themicroprocessor 810 with three types of information. First, a signalindicating that a channel has been identified is provided to themicroprocessor 810 through input line 640. Second, a signal indicatingsignal strength of the identified channel is provided to themicroprocessor 810 through input line 630. Third, a signal indicatingthe format of the identified channel is provided to the microprocessor810 through input line 620.

The signal indicating that a channel has been identified is created bypassing the coupled downstream bandwidth though a band pass filter 650to remove extraneous noise, a signal level detector 660 to convertsignal into a voltage, and another signal level detector 670. The signalleaving the signal level detector 670 is compared to a predeterminedthreshold voltage using comparator 680. The predetermined thresholdvoltage is created using a voltage source 690 and an resistive divider700, and is set such that if the voltage associated with the coupleddownstream bandwidth at the tuner frequency is greater than thethreshold voltage, it is likely a channel in use by the supplier 20,whereas if the voltage associated with the coupled downstream bandwidthat the tuner frequency is less than the threshold voltage, it is likelyinterference signals.

The signal indicating signal strength is created similarly to the signalindicating that a channel has been identified. The signal indicatingsignal strength passes through comparator 720 when it is greater than athreshold voltage created by a voltage source 730 and a resistivedivider 740. To clarify the differences, the signal indicating that achannel has been identified may not have any direct relation to theactual signal strength, whereas the signal indicating signal strength isdirectly proportional to the actual signal strength of the identifiedchannel.

The signal indicating the format of the identified channel is createdwhen the coupled downstream bandwidth passes through a channel analyzer,which includes the band pass filter 650, the signal level detector 660,a synch detector 750, a low pass filter 760, and a signal level detector770. The resulting signal identifies whether the identified channel isan analog format channel or anther type of signal format.

According to current signal transmission specifications, digital formatchannels have a signal strength that is typically 6 dB less than acorresponding analog channel. Accordingly, the microprocessor 810 mustinclude a level offset calculation that can account for this 6 dBdifference when comparing the relative signal strengths of the low andhigh band signal channels 1250, 1260. If this inherent difference is notaccounted for, any resulting comparisons of the two channels 1250, 1260for the purpose of determining relative signal strengths wouldnecessarily be flawed. For example, if the high band channel 1260 isdigital while the low band channel 1250 is analog, the additional,inherent 6 dB difference would incorrectly indicate that there is moreparasitic losses than there actually is. Similarly, if the high bandchannel 1260 is analog and the low band channel 1250 is digital, anyresulting comparison would incorrectly indicate that there is lessparasitic loss that there actually is. Therefore, it should beunderstood that it does not matter whether the 6 dB offset is added tothe signal strength of a digital format channel or the 6 dB offset issubtracted from the signal strength of an analog format channel.Further, it should be understood that the 6 dB offset can be added tothe signal strength of both the low and high band channels 1250, 1260 ifthey are both digital or the 6 dB offset can be subtracted from thesignal strength of both the low and high band channels 1250, 1260 ifthey are both analog. Even further, it should be understood that theoffset value is dictated by the standards observed by a particularsupplier and can be, therefore, a value other than 6 dB.

After completing the scanning process and the process of adding/removingany offsets, the microprocessor 810 now has a low band signal strength(including any offset), a low band channel frequency, a high band signalstrength (including any offset), and a high band channel frequency. Theknown information (i.e., the strength and frequency) of the low and highband channels 1250, 1260 are now compared, by the microprocessor 810, toa predetermined signal strength loss curve (i.e., a gain loss curve),which corresponds to the known parasitic losses associated with the typeof coaxial/optical cables used, as shown in FIG. 9. This stepbeneficially allows the known information to be interpolated across theentire downstream bandwidth. Using the interpolated curve, themicroprocessor 810 determines how much signal level adjustment to applyand in what manner to apply the level adjustment across the entiredownstream bandwidth such that the a resulting gain curve across theentire bandwidth is nearly linear and preferably with a slight increasein gain toward the higher frequencies in anticipation of parasiticlosses that will occur downstream from the premise device 100. Forexample, the amount of level is determined by the high band signalstrength (i.e., high band gain) including any interpolation to thehighest frequency, and the amount of level reduction is determined bythe low band signal strength (i.e., low band level) including anyinterpolation to the lowest frequency.

It should be understood that parasitic losses affect higher frequenciesmore than lower frequencies. Accordingly, if a known signal having a −10dB signal strength, for example, is transmitted at various frequenciesacross the entire downstream bandwidth and across a length ofcoaxial/optical cable, a plot of the resulting gain curve would resultin a curve, which is known. Because the end goal is to have a gain curvethat is a straight line near the original signal strengths or to have again curve that has an increasing slope versus frequency, themicroprocessor 810 directly controls the variable slope adjustmentcircuit to adjust the downstream signal transmission in curve such thatthe lower frequencies are lower in amplitude than the higherfrequencies.

For example, as shown in FIG. 9, using the known frequency and signalstrength for each of the low band channel 1250 and the high band channel1260, a gain curve 1210 can be plotted across the entire downstreambandwidth, which is shown, for example, as being from 50 MHz to 1000MHz. The microprocessor 810 then determines a total amount of leveladjustment to be added by the amplifier 490 and/or the amplifier 500that will at least replace the loss at the highest frequency. In thepresent example, the amount of level adjustment would be at least +38dB, resulting in a gain curve 1220 that is shown in FIG. 10. Based onthe interpolated gain curve shown in FIG. 9, the microprocessor 810instructs the variable slope circuit 460 to apply a similar, butinversely curved amount of correction to result in a relatively flatgain curve 1230 shown in FIG. 10. It may be desirable to increase theamount of level adjustment applied and increase the curvature of theslope adjustment to result in a gain curve 1240, as shown in FIG. 8,which has an increasing slope toward the higher frequencies.

As with the other devices discussed above, the downstream bandwidthoutput level and/or output level tilt compensation device 3 can beactivated automatically upon initialization of the premise device 100, aset intervals, upon the occurrence of a particular event, and/or uponreceipt of an information signal (e.g. a tone, a coded operating signal,etc.) from the supplier 20.

While the present invention has been particularly shown and describedwith reference to certain exemplary embodiments, it will be understoodby one skilled in the art that various changes in detail may be effectedtherein without departing from the spirit and scope of the invention asdefined by claims that can be supported by the written description anddrawings. Further, where exemplary embodiments are described withreference to a certain number of elements it will be understood that theexemplary embodiments can be practiced utilizing either less than ormore than the certain number of elements.

1. A downstream bandwidth output level and/or output level tiltcompensation device that can be inserted into a signal transmission lineof a CATV system on a premise of a user, the device comprising: a tunerconfigured to scan a downstream bandwidth to identify a low band signalchannel and a high band signal channel; a channel analyzer configured todetermine a format of each of the low band channel and the high bandchannel; a signal measurement device configured to measure a low bandsignal strength of the low band channel and a high band signal strengthof the high band channel; an offset circuit configured to perform atleast two of (i) add an offset value to the low band signal strengthwhen the low band channel is a digital format, (ii) subtract an offsetvalue from the low band signal strength when the low band channel is ananalog format, (iii) add an offset value to the high band signalstrength when the high band channel is the digital format, and (iv)subtract a gain offset value from the high band signal strength when thehigh band channel is the analog format; a microprocessor configured tocompare the low band signal strength and the high band signal strength,including any offset values, to a predetermined signal strength losscurve; a variable output level compensation device; and a variable slopeadjusting circuit.
 2. The device of claim 1 wherein the variable outputlevel compensation device and the variable slope adjusting circuit areconfigured such that a gain associated with the high band channel isgreater than a gain associated with the low band channel.
 3. The deviceof claim 1 wherein the predetermined signal strength loss curve is astandard loss curve representative of the transmission line used on ornear the premise of the CATV subscriber.
 4. The device of claim 1wherein the tuner is configured to scan from a maximum frequency towardlower frequencies to find the high band channel, and is configured toscan from a minimum frequency toward higher frequencies to find the lowband channel.
 5. The device of claim 1 wherein an amount of signal leveladjustment provided by the variable output level compensation device isdetermined based on the high band signal strength.
 6. The device ofclaim 1 wherein an amount of slope adjustment provided by the variableslope adjusting circuit is determined based on the low band signalstrength.
 7. The device of claim 1 wherein the signal measurementcircuit is arranged to measure the high band signal strength and the lowband signal strength downstream from the variable output levelcompensation device.
 8. A method for conditioning a downstream bandwidthon a premise of a user of CATV services, the method comprising:receiving a downstream bandwidth from a CATV supplier; scanning thedownstream bandwidth to obtain a low band channel and a high bandchannel; measuring a low band signal strength of the low band channeland a high band signal strength of the high band channel; determining aformat of the low band channel; determining a format of the high bandchannel; offsetting one of the low band signal strength and the highband signal strength by a predetermined offset value when one of the lowband channel and the high band channel is an analog format and one ofthe low band channel and the high band channel is a digital format;comparing the low band signal strength, and the high band signalstrength, including any offset values, to a predetermined signalstrength loss curve; providing an amount of output level compensation;and providing an amount of slope adjustment.
 9. The method of claim 8wherein the amount of slope adjustment is such that a gain associatedwith the high band channel is greater than a gain associated with thelow band channel.
 10. The method claim 8 wherein the predeterminedsignal strength loss curve is a standard loss curve representative of asignal transmission line used on or near a premises of a subscriber. 11.The method of claim 8 wherein the scanning is performed such that a scanbegins from a maximum frequency and extends toward lower frequencies tofind the high band channel, and such that a scan begins from a minimumfrequency and extends toward higher frequencies to find the low bandchannel.
 12. The method of claim 8 wherein the amount of output levelcompensation is determined based on the high band signal strength. 13.The method of claim 8 wherein the amount of slope adjustment isdetermined based on the low band signal strength.
 14. A CATV system forsupplying CATV services from a supplier to a plurality of users, thesystem comprising: at least one discrete downstream bandwidth outputlevel and/or output level tilt compensation device that can be insertedinto a signal transmission line of the CATV system on a premise of eachuser, each device being inserted into the signal transmission line andeach device comprising: a tuner configured to scan a downstreambandwidth to identify a low band signal channel and a high band signalchannel; a channel analyzer configured to determine a format of each ofthe low band channel and the high band channel; a signal measurementdevice configured to measure a low band signal strength of the low bandchannel and a high band signal strength of the high band channel; anoffset gain circuit configured to perform at least two of (i) add anoffset value to the low band signal strength when the low band channelis a digital format, (ii) subtract an offset value from the low bandsignal strength when the low band channel is an analog format, (iii) addan offset value to the high band signal strength when the high bandchannel is the digital format, and (iv) subtract an offset value fromthe high band signal strength when the high band channel is the analogformat; a microprocessor configured to compare the low band signalstrength and the high band signal strength, including any offset values,to a predetermined signal strength loss curve; a variable output levelcompensation device; and a variable slope adjusting circuit.
 15. Thesystem of claim 14 wherein the variable output level compensation deviceand the variable slope adjusting circuit are such that a gain associatedwith the high band channel is greater than a gain associated with thelow band channel.
 16. The system of claim 14 wherein the predeterminedsignal strength loss curve is a standard loss curve representative ofthe transmission line used on or near the premises of the CATVsubscriber.
 17. The system of claim 14 wherein the tuner is configuredto scan from a maximum frequency toward lower frequencies to find thehigh band channel, and is configured to scan from a minimum frequencytoward higher frequencies to find the low band channel.
 18. The systemof claim 14 wherein an amount of signal level adjustment provided by thevariable output level compensation device is determined based on thehigh band signal strength.
 19. The system of claim 14 wherein an amountof slope adjustment provided by the variable slope adjusting circuit isdetermined based on the low band signal strength.
 20. The system ofclaim 14 wherein the signal measurement circuit is arranged to measurethe high band signal strength and the low band signal strengthdownstream from the variable output level compensation device.